This invention relates generally to injection molding and more particularly to injection molding apparatus having an unheated sealing and conductive member with a conductive hot tip shaft extending through an outer sealing collar mounted directly between a heated melt distribution manifold and a cooled cavity plate.
Multi-cavity hot runner injection molding systems require a heated melt distribution manifold in which the melt passage branches towards the various gates through the cooled cavity plate. It is well known in the art to mount nozzles or probes having an electrical heating element to extend from the heated manifold into the cooled cavity plate to provide heat to the melt as it flows from the melt passage to the gates. The distinction between a nozzle and a probe is that the melt flows through a nozzle, whereas it flows around a probe. An example of a configuration using a heated probe is shown in the applicant's Canadian patent number 1,198,266 which issued Dec. 24, 1985. While injection molding molds can have various configurations with numerous plates for different applications, the term "cavity insert" is used herein to indicate any plate or member through which the gate extends to the cavity, although in many other applications it may be called a cavity plate.
In configurations having heated nozzles abutting against the heated manifold, it is also known to mount a hot tip seal at the forward end of each nozzle. Examples of this in which the hot tip seal has a central pin portion or shaft in alignment with the gate are shown in the applicant's U.S Pat. No. 4,279,588 which issued Jul. 21, 1981 and U.S. Pat. No. 4,450,999 which issued May 29, 1984 as well as U.S. Pat. No. 4,266,723 to Osuna-Diaz which issued May 12, 1981. Similarly, the applicant's U.S. Pat. No. 4,810,184 which issued Mar. 7, 1989 and U.S. Pat. No. 5,028,227 which issued Jul. 2, 1991 show an unheated ribbed torpedo assembly mounted between the forward end of each nozzle and a gate insert. However, all of these prior arrangements have the disadvantage that separate nozzles or probes having their own electrical heating element are required in addition to the heated manifold. Also, the requirement of nozzles or probes extending from the manifold limits reduction in mold height, which has become an important consideration in many applications.
The applicant's U.S. Pat. No. 4,303,382 which issued Dec. 1, 1981 discloses a heated nozzle having a forward tip portion with spiral channels which extend around a valve pin to impart a swirling motion to the melt flowing into the cavity. Similarly, the apparatus described in the applicant's Canadian patent number 1,165,525 which issued Apr. 17, 1984 requires a heated nozzle having spiral blades to impart a swirling motion to the melt. Thus, all of the above prior apparatus has the disadvantages that it is relatively costly to manufacture, subject to malfunction, and requires additional mold height to install.